Various apparatus that mix and/or distribute fluid as it flows through a vessel containing solid particles are well known in the art. One or more such devices may be positioned within a vessel and divide the solid particles into two or more beds. The use of such fluid distributing devices can increase the efficiency of operations by providing more uniform fluid properties across the cross-sectional area of the vessel. For example, they can minimize or eliminate flow rate variations or channeling; temperature differences; and variations in the fluid composition. These apparatus may also include a wide variety of means to introduce a fluid stream into the vessel and/or withdraw a fluid stream from the vessel. Such devices will be called “mixer-distributor-collectors”.